Significant increase in the efficiency and speed of atmospheric pressure chemical ionization (APCI) in tandem mass spectrometry (MS/MS) will have a profound impact on its applications to the entire analytical field of characterization of drugs, metabolites, lipids, steroids, etc. A broad applicability of APCI-based MS analysis makes it a unique analytical tool specifically targeting trace amounts of many chemical and biological substances. We plan to build a novel APCI ion source based on atmospheric dielectric barrier discharge (DBD) to significantly improve efficiency and specificity of ACPI-MS based detection method.